An object of metallurgical processes is to set a homogeneous analysis and temperature of the metal melt in the casting ladle. The convective currents in the ladle due to differences in density proceed too slowly and in practical operation have to be accelerated by introduction of inert flushing gases. An improved intermixing is often carried out by blowing in argon or nitrogen through porous bed stones or via lances.
Even in the well-known pneumatic lance-injection process e.g. for desulphurization of pig iron, the carrier gas not only provides the pneumatic transport of the fine-grained solids but at the same time also results in a homogeneous dispersion of the additives in the melt.
The development of the cored wire technique in secondary metallurgy has replaced pneumatic injection in some areas. The absence of a gas which generates turbulence is a disadvantage for many applications in particular for the injection of materials which do not develop their own vapor pressure. The homogenization of the melt occurs too slowly. Concentration peaks occur in the vicinity of the wire as it dissolves which lead to undesired reaction products or even to reductions in yield.
In German Offenlegungsschrift No. 41 03 197 A1 a process is described for the rapid cooling of a metallurgical melt with a wire which is suitable for this that is composed of a metal sheath made of a low-carbon steel sheet for example and a filling made of a granulate in which the melt, wire sheath and wire filling are comprised of essentially the same material. Although the introduction of this wire onto the bottom of the ladle causes a rapid release of the granulate particles in the lower region of the melt, however, the small particle size of 0.2 to 0.5 mm results in a rapid melting of the granulate particles and thus the main cooling effect is restricted to the vicinity of the ladle bottom. The cooled parts of the melt are only more or less homogeneously dispersed by the normal movement of the bath.
In this process the dispersion of the components of the wire filling in the melt thus depend exclusively on the thermal movement of the bath or on the vapor pressure of the filling materials of the wire. Since in leads to materials being introduced into the melt the cored wire injection which have a low or no vapor pressure, an additional dispersing effect by gas generation does not take place when porous gas purge stones are not present which is a disadvantage for a number of practical applications.
Addition of substances to metal melts that split off gas is also known. Of the known gas releasers that are possible for this purpose, limestone and flame coal lead to detrimental changes in the quality of the melts. Limestone thermally splits off carbon dioxide and due to these oxidizing conditions influences for example the steel analysis by burning of aluminum; also reactions with other additives cannot be ruled out. Flame coal also alters the steel analysis by carburizing processes; natural flame coal in addition always contains undesired amounts of oxygen.
The use of polyethylene as a solid compound which splits off ethene is already described in German Patent 22 52 796. However, it is there used as one of several components of a desulfurization composition for raw iron and ferro-alloy melts, which is introduced into the melt bath with the aid of the above mentioned lance process by means of a carrier gas stream. The main object of the polyethylene in this case is the creation of reducing conditions in the iron melt.